1. Field of the Invention
The invention generally relates to processing digitally modulated signals received in a communication system such as a WLAN (Wireless Local Area Network) system, and in particular to a receiver and an operation method that may be used for estimating the power of a received signal to compensate input power changes and to keep the receiver output constant.
2. Description of the Related Art
A wireless local area network is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN. Using radio frequency or infrared technology, WLAN systems transmit and receive data over the air, minimizing the need for wired connections. Thus, WLAN systems combine data connectivity with user mobility.
Most WLAN systems use spread spectrum technology, a wide-band radio frequency technique developed for use in reliable and secure communication systems. The spread spectrum technology is designed to trade-off bandwidth efficiency for reliability, integrity and security. Two types of spread spectrum radio systems are frequently used: frequency hopping and direct sequence systems.
The standard defining and governing wireless local area networks that operate in the 2.4 GHz spectrum, is the IEEE 802.11 standard. To allow higher data rate transmissions, the standard was extended to the 802.11b standard, that allows data rates of 5.5 and 11 Mbps in the 2.4 GHz spectrum. This extension is backwards compatible as far as it relates to the direct sequence spread spectrum technology, and both standards adopt various digital modulated techniques.
A digitally modulated signal in a wireless local area network has to be processed to compensate the influence of disturbances and to keep the output power constant. For compensating power changes in the input digitally modulated signal, usually an automatic gain control loop unit is provided in the receiver. A typical block diagram of such an automatic gain control loop unit is illustrated in FIG. 1. The unit of FIG. 1 comprises an amplifier 100 and a feedback loop having a power calculation unit 110 and a gain control unit 120. The power calculation unit 110 calculates the current power of the output signal of said amplifier 100, and the gain control unit 120 delivers a gain control signal to the amplifier 100.
The amplitude or power of any digitally modulated signal may be represented by I (in-phase) and Q (quadrature-phase) values and the I and Q values can be displayed in a complex diagram. The I value represents the real part and the Q value represents the imaginary part of the signal. When the power calculation unit 110 calculates the output power it has to calculate a square root of the sum of the squared I value and the squared Q value for each received pair of I and Q values. The conventional techniques for calculating the output power comprise unnecessary and complicated calculation steps. In particular the calculation of the squared I and Q components and the calculation of the square root is disadvantageous. It has been found that circuits used for calculation of the power are needed to be of significant complexity and are therefore responsible for high development and manufacturing costs.